The invention relates generally hybrid energy systems and methods for use in connection with diesel-electric locomotives. In particular, the invention relates to a system and method for manufacturing and/or retrofitting diesel-electric locomotives to include a capability to selectively store and transfer electrical energy, such as dynamic braking energy, produced by such locomotives.
FIG. 1A is a block diagram of an exemplary prior art locomotive 100. In particular, FIG. 1A generally reflects a typical prior art diesel-electric locomotive such as, for example, the AC6000 or the AC4400, both or which are available from General Electric Transportation Systems. As illustrated in FIG. 1A, the locomotive 100 includes a diesel engine 102 driving an alternator/rectifier 104. As is generally understood in the art, the alternator/rectifier 104 provides DC electric power to an inverter 106 which converts the AC electric power to a form suitable for use by a traction motor 108 mounted on a truck below the main engine housing. One common locomotive configuration includes one inverter/traction motor pair per axle. Such a configuration results in three inverters per truck, and six inverters and traction motors per locomotive. FIG. 1A illustrates a single inverter 106 for convenience.
Strictly speaking, an inverter converts DC power to AC power. A rectifier converts AC power to DC power. The term converter is also sometimes used to refer to inverters and rectifiers. The electrical power supplied in this manner may be referred to as prime mover power (or primary electric power) and the alternator/rectifier 104 may be referred to as a source of prime mover power. In a typical AC diesel-electric locomotive application, the AC electric power from the alternator is first rectified (converted to DC). The rectified AC is thereafter inverted (e.g., using power electronics such as IGBTs or thyristors operating as pulse width modulators) to provide a suitable form of AC power for the respective traction motor 108.
As is understood in the art, traction motors 108 provide the tractive power to move locomotive 100 and any other vehicles, such as load vehicles, attached to locomotive 100. Such traction motors 108 may be AC or DC electric motors. When using DC traction motors, the output of the alternator is typically rectified to provide appropriate DC power. When using AC traction motors, the alternator output is typically rectified to DC and thereafter inverted to three-phase AC before being supplied to traction motors 108.
The traction motors 108 also provide a braking force for controlling speed or for slowing locomotive 100. This is commonly referred to as dynamic braking, and is generally understood in the art. Simply stated, when a traction motor is not needed to provide motivating force, it can be reconfigured (via power switching devices) so that the motor operates as a generator. So configured, the traction motor generates electric energy which has the effect of slowing the locomotive. In prior art locomotives, such as the locomotive illustrated in FIG. 1A, the energy generated in the dynamic braking mode is typically transferred to resistance grids 110 mounted on the locomotive housing. Thus, the dynamic braking energy is converted to heat and dissipated from the system. In other words, electric energy generated in the dynamic braking mode is typically wasted.
It should be noted that, in a typical prior art DC locomotive, the dynamic braking grids are connected to the traction motors. In a typical prior art AC locomotive, however, the dynamic braking grids are connected to the DC traction bus because each traction motor is normally connected to the bus by way of an associated inverter (see FIG. 1B). FIG. 1A generally illustrates an AC locomotive with a plurality of traction motors; a single inverter is depicted for convenience.
FIG. 1B is an electrical schematic of a typical prior art AC locomotive. It is generally known in the art to employ at least two power supply systems in such locomotives. A first system comprises the prime mover power system that provides power to the traction motors. A second system provides power for so-called auxiliary electrical systems (or simply auxiliaries). In FIG. 1B, the diesel engine (see FIG. 1A) drives the prime mover power source 104 (e.g., an alternator and rectifier), as well as any auxiliary alternators (not illustrated) used to power various auxiliary electrical subsystems such as, for example, lighting, air conditioning/heating, blower drives, radiator fan drives, control battery chargers, field exciters, and the like. The auxiliary power system may also receive power from a separate axle driven generator. Auxiliary power may also be derived from the traction alternator of prime mover power source 104.
The output of prime mover power source 104 is connected to a DC bus 122 which supplies DC power to the traction motor subsystems 124A-124F. The DC bus 122 may also be referred to as a traction bus because it carries the power used by the traction motor subsystems. As explained above, a typical prior art diesel-electric locomotive includes four or six traction motors. In FIG. 1B, each traction motor subsystem comprises an inverter (e.g., inverter 106A) and a corresponding traction motor (e.g., traction motor 108A).
During braking, the power generated by the traction motors is dissipated through a dynamic braking grid subsystem 110. As illustrated in FIG. 1A, a typical prior art dynamic braking grid includes a plurality of contactors (e.g., DB1-DB5) for switching a plurality of power resistive elements between the positive and negative rails of the DC bus 122. Each vertical grouping of resistors may be referred to as a string. One or more power grid cooling blowers (e.g., BL1 and BL2) are normally used to remove heat generated in a string due to dynamic braking.
As indicated above, prior art locomotives typically waste the energy generated from dynamic braking. Attempts to make productive use of such energy have been unsatisfactory. For example, systems that attempt to recover the heat energy for later use to drive steam turbines require the ability to heat and store large amounts of water. Such systems are not suited for recovering energy to propel the locomotive itself. Another system attempts to use energy generated by a traction motor in connection with an electrolysis cell to generate hydrogen gas for use as a supplemental fuel source. Among the disadvantages of such a system are the safe storage of the hydrogen gas and the need to carry water for the electrolysis process. Still other prior art systems fail to recapture the dynamic braking energy at all, but rather selectively engage a special generator that operates when the associated vehicle travels downhill. One of the reasons such a system is unsatisfactory is because it fails to recapture existing braking energy.
Therefore, there is a need for an improved system that captures and stores the electric energy generated in the dynamic braking mode, and that regenerates the stored energy for later use. There is also a need for such an improved system that can be installed as original equipment or installed as part of a retrofit program. There is also a need for such a system that can be installed on a single axle or on multiple axles.
In one aspect, the invention relates to a diesel-electric locomotive system. The system includes a locomotive having an engine. A power converter is driven by the engine and provides primary electric power. A traction bus is coupled to the power converter. The traction bus carries the primary electric power. A first inverter drive is coupled to the traction bus and receives the primary electric power. A first traction motor is coupled to the first inverter drive. The first traction motor has a dynamic braking mode of operation and a motoring mode of operation. The first traction motor generates dynamic braking electrical power which is returned to the traction bus when the operating in the dynamic braking mode. The first traction motor propels the locomotive in response to the primary electric power when operating in the motoring mode. A second inverter drive is coupled to the traction bus and receives the primary electric power. A second traction motor is coupled to the second inverter drive. The system also includes a hybrid energy system. The hybrid energy system comprises an energy storage device that provides secondary electric power. A transfer switch has first and second connection states. The first connection state connects the second inverter drive to the second traction motor. The second connection state connects the energy storage device to the second inverter drive. A switch controller controls the connection state of the transfer switch. When the first traction motor is in the dynamic braking mode of operation and the switch controller places the transfer switch in the second connection state, the second inverter drive transfers a portion of the dynamic braking electrical power to the energy storage device for storage. In this way, the secondary electric power is derived from the portion of the dynamic braking electrical power stored in the energy storage device.
In another aspect, the invention relates to a retrofit system for modifying a diesel-electric locomotive system to operate as a hybrid energy locomotive system. The diesel-electric locomotive system includes a locomotive having an engine. A power converter is driven by the engine and provides primary electric power. A traction bus is coupled to the power converter. The traction bus carries the primary electric power. A first inverter drive is coupled to the traction bus and receives the primary electric power. A first traction motor is coupled to the first inverter drive. The first traction motor has a dynamic braking mode of operation and a motoring mode of operation. The first traction motor generates dynamic braking electrical power which is returned to the traction bus when the operating in the dynamic braking mode. The first traction motor propels the locomotive in response to the primary electric power when operating in the motoring mode. A second inverter drive is coupled to the traction bus and receives the primary electric power. A second traction motor is coupled to the second inverter drive. The retrofit system comprises an energy storage device that provides secondary electric power. A transfer switch has first and second connection states. The first connection state connects the second inverter drive to the second traction motor. The second connection state connects the energy storage device to the second inverter drive. A switch controller controls the connection state of the transfer switch. When the first traction motor is in the dynamic braking mode of operation and the switch controller places the transfer switch in the second connection state, the second inverter drive transfers a portion of the dynamic braking electrical power to the energy storage device for storage. In this way, the secondary electric power is derived from the portion of the dynamic braking electrical power stored in the energy storage device.
In yet another aspect, the invention relates to a method of retrofitting a diesel-electric locomotive system to operate as a hybrid energy system. The diesel-electric locomotive system includes a locomotive having an engine. A power converter is driven by the engine and provides primary electric power. A traction bus is coupled to the power converter. The traction bus carries the primary electric power. A first inverter drive is coupled to the traction bus and receives the primary electric power. A first traction motor is coupled to the first inverter drive. The first traction motor has a dynamic braking mode of operation and a motoring mode of operation. The first traction motor generates electrical power which is returned to the traction bus when the operating in the dynamic braking mode. The first traction motor propels the locomotive in response to the primary electric power when operating in the motoring mode. A second inverter drive is coupled to the traction bus and receives the primary electric power. A second traction motor is coupled to the second inverter drive. The method of retrofitting comprises installing an energy storage device on the locomotive. The energy storage device is constructed and arranged to store electrical power and to provide secondary electric power from the electrical power stored therein. A transfer switch is installed on the locomotive. The transfer switch has first and second connection states. The first connection state connects the second inverter drive to the second traction motor. The second connection state connects the second inverter drive to the energy storage device. The state of the transfer switch is controlled. The transfer switch is selectively placed in the second connection state when the first traction motor is in the dynamic braking mode of operation such that the second inverter drive transfers a portion of the electrical power returned to the traction bus to the energy storage device. The transferred portion of electrical power is stored in the energy storage device.